Variable, high-power microwave power divider



May 23, 1961 c. F. CRAWFORD ET AL 2,985,850

VARIABLE, HIGH-POWER MICROWAVE POWER DIVIDER Filed Nov. 6, 1959 CAPL 5 CR4 WFOPD FIOIAPD E. #701915 INVENTORS Patented May 23, 1961 United States Patent @fiice VARIABLE, HIGH-POWER MICROWAVE POWER DIVIDER Carl F. Crawford and Richard E. Fiore, Haddonfield,

I N.J., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Nov. 6, 1959, Ser. No. 851,481

6 Claims. (Cl. 333-7) This invention relates to microwave power controlling devices and more particularly to a high-power microwave variable attenuator or power divider utilizing a microwave vertebra section in combination with a rotatable circular waveguide section coupled in a fixed or stationary rectangular waveguide system.

Many types of microwave attenuator and power dividers are well known in the art, these well known devices being of the type in which a rotatable section of circular waveguide is coupled in a rectangular waveguide conductor for rotating the electrical field of the microwave energy in the circular waveguide to attenuate the energy or to divide it for rectangular waveguide outputs coupled to the circular waveguide section. Ordinarily, one of the rectangular waveguides, either the input or the output, is made to rotate with the rotatable circular waveguide section, or a rotatable portion of the circular waveguide section has a lateral rectangular waveguide output that must rotate therewith which is a disadvantage in coupling rectangular waveguides in a system a part of which must be rotated with a part of the attenuator or divider device. Where the rectangular waveguide input and output sections are stationary, the known devices use an electromagnetic rotating field means fixed externally of the circular waveguide section and these devices ordinarily require a ferrite element within the waveguide which must be suspended by a low loss dielectric material in order to produce rotation of the electrical field of the. microwave energy. The latter attenuator or power divider devices have a greater loss factor and are certainly more expensive to build than the first-mentioned device as well as having limitations as to power handling capabilities without cooling equipment. Other well known attenuators use resistive strips adjustable within the ,waveguide but such attenuators are for low power and are not considered material herein.

In the present invention, input and output rectangular waveguide sections are fixed against rotative movement thereof so that they may be permanently fixed in a rectangular waveguide system. The attenuator device consists of a rectangular waveguide vertebra section having one end fixed to the fixed rectangular waveguide input and the other end thereof fixed to one end of a rotatable portion of a circular waveguide section, the stationary portion of the circular waveguide Section being fixed to the fixed rectangular waveguide output. The fixed portion of the circular waveguide may have a rectangular waveguide output whereby attenuation may be controlled in the two rectangular waveguide outputs. For simplicity in control of the device the rectangular waveguide input is fixed in a forty-five degree angular relation with respect to the rectangular waveguide output so that the rotatable portion of the circular waveguide may be rotated in either angular direction within forty-five degrees to produce complete attenuation or power division control of the microwave energy. The coupling of the output end of the rectangular waveguide vertebra section to the input end of the rotatable portion of the circular waveguide produces a skewed rectangular waveguide passage into the circular waveguide section except when the rotatable portion thereof is in its intermediate or neutral position wherein the rectangular waveguide vertebra section is aligned. In the present invention the voltage standing wave ratio (VSWR) remains sufliciently low so that any input device or any transmitting device will not adversely aifect the primary function of the device itself; that is, the impedance is substantially constant. It is, therefore, a general object of this invention to provide a high-power microwave variable attenuator or power divider which is controllable for microwave energy passed therethrough from fixed or stationary rectangular waveguide input and output sections.

These and other objects, features, uses, and the attendant advantages will become more apparent to those skilled in the art as the description proceeds and considered along with the accompanying drawing, inwhich:

Figure 1 illustrates a preferred embodiment of the assembled attenuator or divider adjusted in one of its extreme positions,

Figure -2 illustrates an exploded view of the relative position of the rectangular waveguide vertebra elements for the adjustable position of the rotatable circular waveguide portion of Figure 1,

Figure 3 illustrates the attenuator or power divider as shown in Figure 1 but with the rotatable circular waveguide portion adjusted in its other extreme position, and

Figure 4 illustrates an exploded view similar to that of Figure 2 but with the rectangular waveguide vertebra parts positioned in correspondence with the rotatable circular waveguide portion position as shown in Figure 3.

Referring more particularly to Figures 1 and 2, a

microwave variable high-power attenuator or power di-- vider is illustrated as a unit by the reference character 10 which has a rectangular waveguide input section 11 and a rectangular waveguide output section 12 fixed or attached thereto in any well known manner. As illustrated, the rectangular waveguide output section 12 is shownwith the broad sides thereof lying in a horizontal plane and the broad side of the rectangular waveguide input section 1 1 resting in a plane forty-five degrees. with the horizontal plane. The rectangular waveguide section- 11 is coupled to a rectangular waveguide vertebra section 13 as by coupling flanges 14 or any other suitable means well understood in the art. The output end of the rectangular .waveguide vertebra section 13 is coupled by flanges 15 or other suitable means to the input end of a circular waveguide section 1 6, the input end of the circular waveguide section having a rotatable portion 17 with respect of the circular waveguide section. A second rectangular waveguide output may be coupled to the stationary or fixed portion of the circular waveguide section and is. herein illustrated as being a rectangular waveguide sec-v tion 21 vertically positioned on the circular portion 18 with the broad sides thereof paralleling the longitudinal center line of the circular waveguide section. Microwave energy, propagating in the TE mode is conducted through the rectangular waveguide input section 11 and transduced, as is well understood by those skilled in the art, to the TE mode within the circular Waveguide section and is thereafter conducted in the TE mode through the outlets -12 and 21 in accordance with the attenuation. or power divider adjustments of the rotatable. circular aseaeso waveguide portion 17. When the adjusting handle 20 is in its intermediate position in which it is at a right angle position to the broad sides of the rectangular waveguide input section 11, the microwave frequencies will be power divided approximately equal between the outlets 12 and 21 as will hereinafter be made clear.

The rectangular waveguide microwave vertebra section 13 has a plurality of discs a, b, c, and d, which are arranged in a relatively rotatable juxtaposed position and retained in this position by any suitable means. The particular construction and arrangement of the vertebra section is only illustrated herein for the purpose of this invention, no efiort being made to show a complete precision item since commercial items are sufiiciently shown and described in textbooks or catalogs one of which is being referred to herein for such description in Microwave Components by Carl W. Schutter in three volumes. For the purpose of illustration herein the discs 0, b, c, and d are controlled in their relative rotative movements by a strap 25 that is pivotally connected to a pin in the circumference of each of the discs a to d the input end of which is pivotally anchored to the flange 14 or other member fixed with respect to the rectangular waveguide input section 11, and the other end is pivotally anchored at 26 to the flange 15 or other member fixed with respect to the rotatable portion 17 of the circular waveguide section 16. From the foregoing it may be realized that upon adjustable rotation of the handle 20 the several vertebra discs a to d will be progressively rotated in angular relation and the angular displacement relation can be obtained by the placement of the pivotal connections 25-26 on the discs.

The angular relation of the vertebra discs a to d may best be understood by Figure 2 wherein an exploded view of these discs are shown positioned in the condition in which the handle 20 and strap 25 are positioned as shown in Figure 1. Each disc has a rectangular waveguide passage 27 therethrough which, in the assembled condition as shown in Figure 1, will produce a straight rectangular waveguide passage when the handle 20 is at right angles to the broad sides of the rectangular waveguide input 11 or will produce a skewed rectangular waveguide passage in either angular direction as the rotatable portion section 17 of the circular waveguide section is rotated on either side of its neutral position. As viewed in Figure 2, the vertebra discs are positioned to skew the rectangular waveguide input in a clockwise direction as seen from the microwave energy input end wherein the operating handle 20 is in its extreme vertical position. In the position of handle 20 as shown in Figure 1, the electrical field of microwave energy in the TE mode entering through the rectangular waveguide input 11 shown by the arrows will be transduced to the TE mode electric field within the circular waveguide section which electric field will be predominately vertical as shown in dotted lines within the rotatable and stationary portions 17 and 18 of the circular waveguide 16. This electric field is in the proper direction to establish a substantially full power electrical field in the transduced TE mode in the rectangular waveguide output 12. The attitude of the predominately vertical electric field in the TE mode will prevent the microwave energy from entering the lateral rectangular waveguide output 21. Consequently, in the position of the rotatable portion 17 and the handle 20 in Figure 1 the microwave energy conducted into the rectangular waveguide input section 11 is conducted substantially full power through the rectangular waveguide output 12, the only attenuation being that of inaccuracies in the construction of the inner walls of the waveguide and the slight projections caused by the vertebra disc passages 27. While the vertebra discs a to d could be rotated such that they retain an equal angular difference between adjacent discs, it has been found preferable to actuate these discs through the strap 25 and the pivoted connections 26 such that the discs a and d are able to rotate plus or minus nine degrees and the discs b and c to rotate plus or minus thirteen and one-half degrees with respect to each other. It is also important that the longitudinal length of the discs and particularly the rectangular waveguide passages 27 be about one-quarter wavelength of the microwave energy transmitted to provide good design characteristics of the conducted microwave energy. Also, while four such discs are shown and described as constituting the vertebra section 13 with the preferred maximum angular relationship, it is to be understood that a greater number of such discs or possibly a lesser number may be used without departing from the spirit of this invention.

Referring more particularly to Figures 3 and 4, wherein like reference characters are used for like parts as shown in Figures 1 and 2, it is to be noted that the rotatable portion 17 of the circular waveguide section is in its extreme counter-clockwise position in which the discs 0 to d of the vertebra section are each in their extreme counter-clockwise position as illustrated in the exploded view of Figure 4. In the adjusted position as shown in Figure 3 the electric field of the microwave energy in the TE mode conducted through the rectangular waveguide input section 11 is rotated so that the attitude thereof is predominately in the horizontal plane in the TE mode within the circular waveguide section 16. Since the electric field of the microwave energy in the TE mode within the circular waveguide section 16 is paralleling the broad sides of the rectangular waveguide output section 12, no microwave energy in the TE mode can be established in the waveguide out put 12 whereby microwave energy to output 12 is cut off. Under the same conditions the electric field in the circular waveguide section 16 is proper to establish an electric field in the 'TE mode in the lateral output 21 whereby substantially full power of the microwave energy applied to the input 11 is conducted through the output 21. As may now be well understood, adjustment of the rotatable circular portion 17 of the circular waveguide section 16 will inversely attenuate the microwave energy transmitted through the outputs 12 and 21 which may also be stated as producing microwave power division between the outputs 12 and 21. The fo1- lowing equation sets out in general the attenuating action although the results of reflections are not accounted for therein:

db 10 log :3

where P =P cos 0 or P sin 0 P ='=input power P =output power 0=displacement angle The operation of the variable attenuating device is believed to be well understood from the description above. It is to be understood that if the rectangular waveguide output 21 includes a power absorbing branch the microwave energy may be attenuated for the single rectangular waveguide output 12 by adjustment of the handle 20 between its two extrme rotative positions of ninety degrees. By this device the rectangular waveguides 11, 12, and 21 may all be coupled into a stationary system since none of these waveguide inlet or outlet sections are moved or rotated in any manner, the complete operation of attenuating or power dividing the energy being produced solely by the rotating elementsin the waveguide component 10.

While many modifications and changes may be made in the constructional details and features of this invention without departing from the spirit or scope thereof, it is to be understood that we desire to be limited only in the scope of the appended claims.

We claim;

1. A variable, high-power waveguide attenuator comprising: a waveguide section having a rectangular waveguide input and a rectangular waveguide output in alignment on opposite ends of a circular waveguide, said input and output being oriented with the long dimensions thereof at forty-five degrees fixed angular relation; a rotatable portion and a stationary portion in said circular waveguide, said stationary circular waveguide being in fixed relation with said rectangular waveguide output; and a vertebra section of a plurality of relatively rotatable, contiguous discs, each having a rectangular waveguide passage therethrough, coupled between said input and said rotatable portion of said circular waveguide and relatively rotatably connected to be actuated to produce equal angular difference between said rectangular Waveguide passages in all angular positions and to produce a continuous straight rectangular Waveguide in an intermediate rotative position whereby microwaves entering through said input may be variably attenuated for said output by not more than forty-five degrees rotation of said rotatable portion of said circular waveguide from said intermediate position.

2. A variable, high-power microwave attenuator controlling device comprising: a waveguide component having a rectangular waveguide input and a rectangular waveguide output in alignment on opposite ends of a circular waveguide section, said rectangular waveguide input and output being oriented at a fixed forty-five degrees relative angle; a rotatable portion and a stationary portion in said circular waveguide section, said stationary circular waveguide section having a lateral rectangular waveguide outlet thereon and fixed relative to said rectangular waveguide output; and a vertebra section between said rectangular waveguide input and said rotatable portion of said circular waveguide, said vertebra section including a plurality of discs, each about one-quarter wavelength along with a rectangular waveguide passage therethrough and in juxtaposed, relatively rotatable position with connecting means therebetween to maintain equal angular displacement between adjacent discs in all rotatable positions of the vertebra section to provide a continuation of said rectangular waveguide input in one rotatable position and to skew said continuation of rectangular waveguide input in other rotatable positions of said rotatable portion of said circular waveguide section whereby microwave energy from said input is attenuated inversely through said outputs from zero to the level of the input microwave energy upon ninety degree variable control of said rotatable portion of said circular waveguide section.

3. An attenuator device as set forth in claim 2 wherein a microwave energy electric field is transduced from the TE mode to the TB mode in passing from the rectangular waveguide input through said vertebra section into said circular waveguide, and said rotatable portion of said circular waveguide section rotates said TE electric field with respect to said input.

4. A variable, high-power microwave attenuator controlling device comprising: a waveguide component having a rectangular waveguide input for receiving microwave energy of an electric field in the TE mode and a rectangular waveguide output in alignment on opposite ends of a circular waveguide section, said rectangular waveguide input and output having the broad sides thereof oriented and fixed at forty-five degrees angular relation; a rotatable portion and a stationary portion in said circular waveguide section, said stationary circular waveguide portion having a second rectangular waveguide output thereon and being fixed with respect to said firstmentioned output; and a vertebra rectangular waveguide section between said rectangular waveguide input and said rotatable portion of said circular waveguide, said vertebra section including a plurality of juxtaposed and relatively rotatable discs with aligned rectangular waveide passages therethrough of about one-quarter wavelength and actuatably rotatable with substantially equal angular difierence between adjacent discs in all rotatable positions to couple said rectangular input with said circular waveguide rotatable portion to produce a variable skew of said rectangular waveguide input and vertebra section to rotate the electric TE field establishing a variably rotated electric T-E field in said stationary circular waveguide portion whereby microwave energy is attenuated inversely through said rectangular waveguide outputs by variably adjusting said rotatable circular waveguide portion.

5. An attenuator as set forth in claim 4 wherein said rotatable circular waveguide portion is rotatable through ninety degrees, the intermediate rotative position bringing said rectangular waveguide passages of said vertebra discs and said inlet into registry.

6. A variable, high-power microwave attenuator controlling device comprising: a waveguide component having a rectangular waveguide input section for trans mitting microwave energy with an electric field in the TE mode and a rectangular waveguide output section in alignment on opposite ends of a circular waveguide section, said rectangular waveguide input and output sections having the broad sides thereof oriented at fortyfive degrees angular fixed relation; a rotatable portion and a stationary portion in said circular waveguide section, said stationary circular waveguide portion being fixed to said rectangular waveguide output section and having a lateral rectangular waveguide output thereon with the broad sides thereof in planes parallel to the longitudinal centerline of said circular waveguide section; and a vertebra rectangular waveguide section having one end fixed to said rectangular waveguide input section and the other end fixed to said rotatable circular waveguide portion for having rotatable movement imparted thereto to rotate the electric field of microwave energy, said vertebra section having a plurality of rotatably juxtaposed discs with rectangular waveguide passages therethrough of about one-quarter wavelength which are rotated with substantially equal angular difference maintained therebetween to produce a skewed rectangular waveguide passage from the input to said circular waveguide section thereby establishing an electric field TE mode in said circular waveguide section whereby the microwave energy is attenuated inversely through said rectangular waveguide outputs in the TE modes by varying the adjustment of said rotatable circular waveguide portion.

References Cited in the file of this patent UNITED STATES PATENTS Frear Nov. 7, 1950 Zaleski Oct. 30, 1956 OTHER REFERENCES 

